1. Field of the Invention
The present invention relates to a printed circuit board used for various types of electric equipment or electronic equipment.
2. Description of the Background Art
Conventionally, printed circuit boards have been used for various types of electric equipment or electronic equipment. In order to make the electric equipment and the electronic equipment small in size and lightweight, wiring patterns on the printed circuit boards have been made higher in density, and have been placed on the printed circuit boards miniaturized and increased in density.
In recent years, the increase in density of the wiring circuit boards has progressed, as described above, and signals to be handled have been becoming high-frequency digital signals. As a result, crosstalk of the digital signals to adjacent wiring patterns or radiative noise may occur.
Therefore, a method of inhibiting the crosstalk and the radiative noise from occurring by respectively forming conductive films on both surfaces of an insulator in a printed circuit board is proposed (see JP 2004-87627 A).
In the above-mentioned conventional printed circuit board, however, a coupling capacitance increases between a wiring pattern and the conductive films formed on the insulator increases. As a result, a characteristic impedance is significantly reduced, so that the transmission efficiency of a digital signal is reduced.